New windows - what to consider before replacing
Cherwell Windows

5 things to consider before buying windows

From glazing and frame options to planning permissions, what to consider when choosing windows

By Rebecca Foster |

When it comes to choosing new windows for a self-build or renovation project, it’s easy to focus on the aesthetics over planning implications and potential pitfalls.

Consider these five factors before buying new windows, so you can ensure they complement the style of your project and meet building regulations.

1. Window frame options

Thanks to modern techniques, there’s a host of options when it comes to choosing the design and opening configuration of your windows. From traditional casement designs to sleek tilt-and-turn versions, it’s important to research which solution best complements your property.

Metal, timber and PVCu are the main framing materials. PVCu is a budget-conscious choice, available in a number of colours and woodgrain finishes. Expect to pay from £150 per sqm.With its innate character, timber is often the first choice for traditional projects. Well-maintained units offer a service life of 50 years and more. Expect to pay around £200 per sqm for untreated softwood products and £300-plus per sqm for hardwood alternatives.

Metal frames come in bronze, steel and aluminium. ‘For a modern look, aluminium windows are generally used more often as they offer a slimmer profile than timber units,’ says David Flower, a director at FlowerKittle Architects. ‘Composite products with an aluminium finish on the exterior and timber on the interior are an alternative.’ These offer the low-maintenance qualities of metal and the characterful warmth of wood.

‘Steel gives the narrowest sightlines for a hinged window and the welded corners create a smooth finish with no mitre joints or junctions. It also offers an artisan industrial style,’ says Rebecca Clayton, director of marketing and communications at IQ Glass. ‘Frameless windows made from structural glass are also available for fixed glazing, with fixings hidden by the building finishes.’

Your choice of frame will also be influenced by the size of window required. ‘Opening windows with heights of up to 1,200mm are available in our slimmest frame choice,’ says Carl Farrow, technical development manager at IDSystems. Anything taller, or triple-glazed, calls for a larger framing profile and a heavier duty hinge that’s capable of withstanding the additional load.’

House with guillotine window frames

Photo: IQ Glass UK

2. Glazing types

Invest as much time and research to the specification of the glass as you would to the framing material. ‘Your choice will usually be driven by a combination of requirements – primarily thermal performance – but also factors such as security, acoustic control and privacy,’ says Donna Muir, sales manager at Velfac Direct. ‘Glass specification must reflect each window’s position and function: enhanced security on the ground floor, for instance, or improved acoustics facing a busy road.’

To comply with Building Regulations, windows should achieve an overall U-value (a measure of heat loss, where lower numbers are better) of 1.8W/m2K. Check that this figure applies to the whole unit, including frame and glass.

Double glazing is usually ample to meet requirements in terms of thermal performance. Typically, triple glazing is specified for schemes prioritising energy performance, such as passivhaus builds.

Low E-coatings (where the ‘E’ stands for emissivity) to reduce heat loss through the glass is often applied to new windows as standard. ‘The almost invisible layer is designed to reflect heat back into the room,’ says Farrow. You can also specify inert gas, such as argon, fillings to boost your windows’ thermal performance.

Your windows will also need to meet Building Regulations Document Q, which is concerned with security. At ground-floor level, all glazed elements should include a laminated layer within the sealed unit that holds the glass together when it’s broken. The same applies to first-floor windows that are easily accessible. ‘If you let your glazier know what performance and characteristics you want, they’ll be able to advise on the spec,’ says Clayton.

3. Planning considerations

Windows play a vital role in establishing the architectural style of your home and will be included in any plans you submit to the local authority.

‘The council will always take into consideration how the windows and the appearance of the building will impact on the surrounding area’s character,’ explains Flower. ‘If you’re looking to install units that aren’t in keeping with the typical properties nearby, you may need to justify how they’re coherent with the overall design.’

From a planning perspective, you will face stricter guidelines if your home is situated in a conservation area or close to a listed property. ‘It doesn’t mean you can’t choose something different, as contrast is sometimes the best approach, but it’s important to be aware of the challenges you may face,’ Flower adds.

House with aluminium casement windows and toughened panes with low e coating

Photo: Klöeber

4. Building regulations

In most scenarios, installing like-for-like replacement windows falls under Permitted Development, so you won’t need to apply for formal consent.

However, some local authorities are stricter than others so it’s always worth checking with the planning department first. And if the proposed windows are significantly larger or of a different style to the originals you may need to get permission. Again, different rates could apply if your property is listed or is situated in a conservation area.

Replacement windows need to conform to Building Regulations, too. In terms of thermal performance, new units should achieve a U-value of 1.6M/m2K. ‘Buildings move over time, and the openings in the external walls will not be completely straight,’ says Flower. ‘A professional installer will ensure the frame sizes are measured to the specifics of the house.’

House extension with window glazing

Photo: Maxlight

5. Learn how to avoid the pitfalls

Factor in factory lead times when it comes to mapping out your build schedule.

‘Projects can be delayed if a client can’t decide on the frame finish,’ says Clayton. ‘This pushes back the start of manufacture, which will hold back the installation and may have a knock-on effect on the construction schedule.’

Thermal performance is another important aspect. Even high-performance, triple-glazed units with all the bells and whistles won’t match the thermal attributes of a well-insulated wall.

To meet the required building standards in terms of overall energy performance, you may need to pack additional insulation into the walls, roof and floors to offset any heat loss via glazing.

Always employ a reputable window installer. Supply-and-fit companies are a smart option, as there’s a clear line of accountability in the unlikely event that something should go wrong.

White tile bathroom with clerestory windows and solar control coating

Photo: ID Systems